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Rocket Cars

In this activity, students construct a balloon-powered rocket car, demonstrating Newton's Third Law of Motion.

Formally stated, Newton's third law is: For every action, there is an equal and opposite reaction.

According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction - a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion.

In this activity, the rocket car is propelled by air escaping from a balloon through a plastic straw. The escaping air acts as the action force, causing the car to roll forward, as the reaction force "pushes" back..

Objectives

  • Understand the concept of action and reaction forces.

Materials

  • For each car:
    One piece of card stock, about 2” x 3” (e.g. a playing card)
    2 straight straws (or one straw cut into two) and 1 bendy straw
    4 discs approx. 5cm in diameter, cut from cardboard or other hard material (film canister lids work well if you can find them)
    2 bamboo skewers
    1 balloon
    Clear tape
    Scissors

Key Questions

  • In what direction is the air escaping?
  • What direction does the car travel in?
  • What is the action force?
  • What is the reaction force?

What To Do

  1. Cut the card stock so it’s about the same size as a credit card
  2. Tape 2 straws across the width of the card, making sure they are parallel. This will be the bottom of your car and the two straws will hold your bamboo “axle”
  3. Tape a bendy straw along the length of the top of the card, with the bend sticking up over the edge of the card.
  4. Poke a skewer through one wheel, slide the skewer through one of your axle straws and poke the other wheel onto the skewer. Do the same with the second skewer and wheels.
  5. Tightly tape the mouth of the balloon over the straight end of the straw.
  6. Blow up the balloon through the bendy end of the straw, and let it go on a smooth surface. How far does it travel?

Extensions

  • Try running your rocket car up an incline. What force must it overcome in order to go up?
  • Try modifying your car so that it can travel uphill.

Other Resources

How Stuff Works| Newton’s Laws of Motion